Dispenser for liquids of varying density



Oct. 7, 1969 .1. BUCHLER 3,471,052

I DISPENSER FOR LIQUIDS OF VARYING DENSITY Filed Sept. 20, 1967 2 Sheets-Sheet i WIIIIIIIlIlltr v 2 I By Attorney l I I V Joseph. Buchler Oct. 7, 1969 H A v 3,471,062-

DISPENSER FOR LIQUIDS OF VARYING DENSITY Filed Sept. 20,1967 2 Sheets-Sheet 2 h v r I NVENTOR.

Atton 'zey' United States Patent Office 3,471,062 Patented Oct. 7, 1969 US. Cl. 222-145 8 Claims ABSTRACT OF THE DISCLOSURE To dispense a liquid of progressively varying (e.g. decreasing) density, for use in a density-gradient sedimentation system, two upwardly diverging frustoconical chambers are disposed side by side with a connecting passage at their bottoms and one or more discharge ports remote from that passage at the bottom of one chamber, a vibratile agitator rod extending axially within the latter chamber almost to the bottom thereof. Upon filling of the two chambers with measured quantities of compatible liquids of diiferent specific gravity (e.g. different concentrations of aqueous solution of a water-soluble substance such as surcrose or CsCl), with the denser liquid initially present in the chamber having the outlet port or ports, the liquid drawn from that chamber is progressively diluted by the contents of the other chamber.

My present invention relates to an apparatus for dispensing a mixture of two related and compatible liquids which are to be present in progressively varying proportions. A typical field of application is the preparation of density gradients for sedimentation systems, the two constituent liquids of the mixture being then a denser and a less dense solution of a given substance (e.g. sucrose or caesium chloride in water).

The general object of my invention is to provide an apparatus for delivering such mixtures in a predictable and reproducible manner.

A more particular object of my invention is to provide a dispenser of this character which will operate satisfactorily over a wide volumetric range.

I have found, in accordance with this invention, that the aforestated objects may be realized by the provision of two upwardly open frustoconical chambers disposed side by side, advantageously in a common block of transparent plastic material, which are interconnected at their bottoms by a passage, one of these chambers (hereinafter referred to as the mixing chamber) being provided at its bottom with one or more outlets remote from the connecting passage. When the mixing chamber is initially filled with, say, a relatively dense solution while the other chamber contains a less dense solution serving as a diluent therefor, the withdrawal of liquid from the mixing chamber will result in a transfer of diluent from the other chamber to the mixing chamber with progressive dilution of the contents of the latter so that the efliuent from the mixing chamber is a progressively less concentrated solution. This effiuent may then be caught in one or more test tubes to form density gradients therein.

In an analogous manner, other compatible constituent liquids may be used to produce, for example, a mixture of progressively varying pH or ionic strength.

In order to insure a maximum of homogenization of the effluent mixture, I prefer to provide the mixing chamber with an agitator advantageously in the form of a vibratile rod extending axially almost to the bottom of that chamber.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a cross-sectional view of a dispenser according to the invention;

FIG. 2 is a top plan view of the dispenser as seen from the line II--II of FIG. 1; and

FIG. 3 is a set of graphs serving to explain the operation of my improved dispenser.

The apparatus shown in the drawing comprises a unitary block 1 of transparent synthetic resin, such as a polyacrylate, having formed therein two upwardly open frusto- .conical chambers 2 and 3. Block 1 is supported on a standard 11 to which it is secured by screws 12 and which also carries an electrically operated vibrator 13 having extending therefrom a stirrer rod 10. This rod, in its quiescent state, is coaxial with mixing chamber 3 and reaches almost to the very bottom thereof. Diluent chamber 2 and mixing chamber 3 are interconnected by a narrow passage 4 which can be closed, during the charging of the cham bers, by a stopcock 5 fitted into the underside of block 1. Two channels 6, 6", representative of any limited number of such outlets, radiate from the bottom of mixing chamber 3 at peripherally spaced locations remote from passage 4 and form ports for the discharge of efiluent into respective test tubes 9', 9". For this purpose, outlet tubes 8, 8", provided with conventional shut-off means, not shown, are inserted into channels 6, 6", and are provided with connectors 7 7 fastening them to the block 1.

In operation, chamber 2 may be filled with a relatively dilute solution of a chosen substance, or even with just a solvent (such as Water) therefor, while chamber 3 receives a preferably equal volume of a relatively concentrated solution of the same substance. Thereafter, stirrer 10 is set in operation, stopcock 5 is rotated to open the passage 4, and outlet tubes 8', 8" are allowed to discharge into test tubes 9 and 9", respectively, e.g. by the removal of clamp valves therefrom. It is also possible to control the discharge by means of a forced-feed pump inserted into each tube 8', 8", the several pumps being suitably synchronized. In any event, the combined capacity of the test tubes 9', 9" should equal or exceed the total volume of liquid introduced into the two chambers 2, 3.

The significance of the conicity of chambers 2 and 3 will now be explained with reference to FIG. 3.

Graph (a) of this figure illustrates the rate of discharge of a cylindrical chamber C through a restricted outlet, in terms of the height h of the liquid level as a function of time t. Graph (12) gives the discharge rate for a frustoconical chamber C (approximating a complete cone), whereas graphs (0) and (d) apply to the discharge of chambers C and C respectively, through a constant-rate pump P.

With a cylindrical chamber C emptying into a restricted outlet of (assumed) constant flow resistance, the drop in liquid level h follows a logarithmic law, expressed by the formula h/H=e where k is a constant and H is the starting level. This theoretical curve approaches zero asymptotically, yet in practice the discharge will terminate at a time T (as indicated in dot-dash lines) since the effective outflow resistance drops for small values of h.

As shown in FIG. 3(b), the change in level during discharge of chamber C (idealized with assumption of perfect conicity and, again, a constant outflow resistance) follows a parabolical curve representing the function h=k /Tt..

If a pump P intervenes in the discharge of cylindrical chamber C then, as shown in FIG. 3(0), the level change follows a linear law h=k(Tt). With a frustoconical chamber C and under the idealizing conditions specified above, the discharge curve follows a cubic equation h=k /'T-t as shown in FIG. 3(d).

If the chambers 2 and 3 of FIGS. 1 and 2 were both cylindrical, and if discharge were by gravity only, the decrease in the level of each chamber would approximate the curve of FIG. 3(a) and would be considerably steeper for larger volumes than for small ones. Since the factor k includes the outflow resistance, and since this resistance may be diflFerent for the passage 4 and for the outlets 6', 6" (apart from being subject to variation with the specific gravity of the liquid), the difference between the discharge rates of the two chambers may be so marked as to lead to appreciable instantaneous differences in liquid level, with the result that the volume of the discharge is not distributed evenly between the two chambers and the desired linearity of the density gradient is not realized. If the discharge from mixing chamber 3 is controlled by a pump, this problem will be aggravated since the outflow from the two chambers will follow widely different laws as illustrated in graphs (a) and (c) of FIG. 3.

With two upwardly diverging chambers, on the other hand, the change in level will be very gradual over a wide volumetric range as represented by the left-hand portion of the curve shown in FIG. 3(b). Equalization between the two chambers is thus greatly facilitated. Moreover, if the liquid is drawn from chamber 3 by a pump, the laws of discharge of the two chambers will not be very dissimilar as will be apparent from a comparison of graphs (b) and (d) of FIG. 3. It is of interest to note that, at least with the idealizing assumptions referred to, the vertex angle of the cone has no influence upon the general law of discharge although, of course, the exact shape of the curve will depend thereon.

For practical purposes, and in order to minimize the length of connecting passage 4, I prefer to use relatively slender chambers with vertex angles on ranging between about and 10. The bottom diameter of each chamber may then range, preferentially, between approximately 5 and 10 mm.

A suitable vibration rate for the agitator rod is on the order of 30 cycles per second.

The rate of density change in the effluent mixture can be controlled through suitable choice of the density of the diluent in chamber 2. If only a single test tube is to be filled, the starting volume in each chamber should be correspondingly reduced. Naturally, three or more test tubes could be simultaneously filled if additional outlets from chamber 3 were provided in block 1,.

I claim:

1. Apparatus for dispensing a mixture of two constituent liquids in progressively varying proportions, comprising two juxtaposed, open-topped, upwardly diverging frustoconical chambers for respectively receiving said constituent liquids, said chambers being provided at their bottoms with a connecting passage, one of said chambers being provided at its bottom with mixing means including said passage and outlet means remote from said passage for mixing and discharging the liquids.

2. An apparatus as defined in claim 1, further comprising agitator means in said one of said chambers.

3. An apparatus as defined in claim 2 wherein said agitator means comprises a vibratile rod extending axially downwardly to substantially the bottom of said one of said chambers.

4. An apparatus as defined in claim 1 wherein said chambers have vertex angles ranging between substantially 10 and 20.

5. An apparatus as defined in claim 4 wherein said chambers have bottom diameters ranging between substantially 5 and 10 mm.

6. An apparatus as defined in claim 1 wherein said outlet means comprises a plurality of tubes communicating with said one of said chambers at peripherally spaced locations.

7. An apparatus as defined in claim 1, comprising a unitary solid block with recesses forming said chambers and with substantially horizontal channels on the level of said bottoms forming said passage and part of said outlet means.

8. An apparatus as defined in claim 7 wherein said block consists of transparent synthetic resin.

References Cited UNITED STATES PATENTS 1,974,988 9/ 1934 Hillstrom 222-243 2,580,521 1/1952 Couchot 222142.1 2,769,576 11/1956 Stevens 222478 3,230,954 1/1966 Burgess et al. 222

ROBERT B. REEVES, Primary Examiner H. S. LANE, Assistant Examiner U.S. Cl. X.R. 23267; 222-154 

